It is of great use for shops and stores to be able to determine how many persons are currently occupying an area, such as a store or department of a store. This may be important for safety reasons and also for security reasons.
A variety of people counting systems are well-known and commercially available. In general, occupancy counting systems are based on the difference between the total number of people walking in and out of the area.
One example of such a system is disclosed in US2006067456 which discloses system for counting a number of people or other moving objects entering or leaving a space has a camera which provides an image of an entrance to the space. A data processor identifies moving objects in the image. The data processor is configured to count people or other objects which enter or leave an area within the image for two or more segments of a boundary of the area. Accuracy of the counting system can be monitored by comparing the counts for the different segments.
A disadvantage is that the counting in both directions will start to diverge from the truth, thus making the error to accumulate over time. The propagated error will be in proportion of the total amount of visitors. Since occupancy naturally has a lower physical upper limit than the total amount of visitors during a day, the error will eventually be large enough to render the estimate void.
Another disadvantage is that this method requires calibration from the user. If it can be established that an area is empty or contains a specific amount of people, the error can be removed. If this kind of reset cannot be made, the accumulated error is never removed.
There is thus a need for a more accurate occupancy estimation which doesn't require user calibration.